CONTRACT REPORT
Comparing Apples, Oranges and Grapefruit:
An Analysis of Current Building Energy Analysis
Standards for Building America, Home Energy Ratings
and the 2006 International Energy Conservation Code
FSEC-CR-1650-06
September 2006
Submitted to:
U.S. Department of Energy
Under Cooperative Agreement
No. DE-FC26-99GO10478
Authors:
Philip Fairey
Carlos Colon
Eric Martin
Subrato Chandra
DISCLAIMER
This report was prepared as an account of work sponsored by an agency of the United
States government. Neither the United States government, nor any agency thereof, nor
any of their employees, makes any warranty, express or implied, or assumes any legal
liability or responsibility for the accuracy completeness, or usefulness of any information,
apparatus, product, or process disclosed, or represents that its use would not infringe
privately owned rights. Reference herein to any specific commercial product, process, or
service by trade name, trademark, manufacturer, or otherwise does not necessarily
constitute or imply its endorsement, recommendation, or favoring by the United States
government or any agency thereof. The views and opinions of authors expressed herein
do not necessarily state or reflect those of the United States government or any agencies
thereof.
ACKNOWLEDGMENTS
This work is sponsored, in large part, by the US Department of Energy (DOE), Office of
Energy Efficiency and Renewable Energy, Building Technologies Program under
cooperative agreement number DE-FC26-99GO10478. This support does not constitute
an endorsement by DOE of the views expressed in this report.
We appreciate the encouragement and support from Mr. George James, Mr. Ed Pollock
and Mr. Bill Haslebacher of DOE.
FSEC-CR-1650-06
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Table of Contents
ABSTRACT....................................................................................................................... 1
EXECUTIVE SUMMARY .............................................................................................. 1
1
INTRODUCTION..................................................................................................... 5
1.1
Background ....................................................................................................... 5
1.2
Objectives........................................................................................................... 5
2
METHODS ................................................................................................................ 6
2.1
Home Selection .................................................................................................. 6
2.2
Performance Comparison ................................................................................ 7
2.2.1
Comparative Analysis Rule Sets.............................................................. 7
2.2.2
Rule Set Differences.................................................................................. 8
2.3
General Analysis Methods ............................................................................. 10
2.3.1
BA Rule Set as the Basis for Analysis ................................................... 14
2.3.2
Additional Modeling Assumptions for Evaluated Homes................... 15
2.3.3
HERS and IECC Figures of Merit ........................................................ 15
3
RESULTS ................................................................................................................ 17
3.1
Revised Benchmark Incremental Analysis................................................... 17
3.2
Comparisons of BA, HERS and IECC Reference Standards ..................... 20
3.2.1
Comparisons of the Reference Home Standards ................................. 21
3.2.2
Comparisons with the 2006 IECC Standard ........................................ 22
3.2.3
Comparisons with the 2006 ENERGY STAR Standard .......................... 23
3.2.4
The HERS Index ..................................................................................... 24
3.3
Impacts of Other Home Characteristics ....................................................... 25
3.3.1
Number of Stories ................................................................................... 26
3.3.2
Foundation Type ..................................................................................... 27
3.3.3
Fuel Type ................................................................................................. 28
3.3.4
Internal Gains ......................................................................................... 29
3.3.5
Energy Uses Other than Code Energy Uses ......................................... 31
3.3.6
Home Size ................................................................................................ 31
3.4
Higher Levels of Energy Efficiency (BA-50) ................................................ 32
4
CONCLUSIONS ..................................................................................................... 34
5
RECOMMENDATIONS........................................................................................ 37
6
REFERENCES........................................................................................................ 39
Appendix A Selected House Plans and Elevations...................................................... 40
Appendix B Housing Characteristics........................................................................... 44
FSEC-CR-1650-06
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ABSTRACT
The purpose of this work is to determine the relationship between the U.S. Department of
Energy’s Building America (BA) Benchmarking Analysis methods and the energyefficiency analysis methods used by the International Energy Conservation Code (IECC)
and the Residential Energy Services Network (RESNET) and the Home Energy Rating
Systems (HERS) industry for similar purposes. Analysis for three different home sizes
conducted in seven different climate zones revealed no correlation between the analysis
methods. Pros and cons are presented for different policy options for maintaining or
changing the BA benchmark.
EXECUTIVE SUMMARY
The overall purpose of the work presented in this report is to determine the relationship,
if any, between the U.S. Department of Energy’s Building America (BA) Benchmarking
Analysis methods and the energy-efficiency analysis methods used by the International
Energy Conservation Code (IECC) and the Residential Energy Services Network
(RESNET) and the Home Energy Rating Systems (HERS) industry for similar purposes.
The IECC allows code compliance through a performance-based comparative analysis
method and the HERS industry uses very similar standards and methods to determine a
relative measure of energy-efficiency performance called the HERS Index.
The simple goal of the work is to be able to say with certainty that a whole-building
HERS Index of ‘x’ corresponds to a BA whole-building % savings of ‘y.’ Similarly, the
goal is to be able to also say with certainty that this BA % savings of ‘y’ corresponds to a
savings of ‘z’ with respect to the IECC minimum code standard.
The study is accomplished using homes of three different sizes (intended to represent
‘typical’ small, medium and large home plan options), on three different foundation types
(slab-on-grade, vented crawlspace and conditioned basement), using both 1-story and 2story models, in all 7 of the contiguous U.S. climate zones identified by the 2006 IECC.
®
The analysis is conducted using version 2.5, release 9 of EnergyGauge USA, RESNET
accredited software, produced and marketed by the Florida Solar Energy Center, for
Home Energy Ratings, IECC performance-based code compliance and federal tax credit
qualification. The basis for the analysis was the Building America Benchmarking
Analysis procedures and all home cases were evaluated in accordance with the methods
of this procedure for the purposes of creating an apples-to-apples comparison.
The results of the analysis are informative, showing not only the differences between the
3 methods of comparing the energy-efficiency performance of buildings, but also the
origins of these differences and their impact on the primary goal of the analysis.
Every effort is made to accomplish the analysis using a consistent set of “rules” for all
three methods, one that results in the ability to state with certainty that on an apples-to-
FSEC-CR-1650-06
1
apples basis, system A corresponds to system B in the following way. However, as the
title of the report suggests, this goal is not achieved. The analysis results and findings do
not support any consistent correlation between the Building America Benchmarking
Analysis procedure and the HERS or IECC analysis procedures. The analysis does show
a reasonably consistent relationship between HERS and IECC but the relationship ends at
that point. Hence, the title of the report, indicating that while two of the analysis methods
are, in fact, citrus fruits, the other is not.
Perhaps the most illustrative example of this finding – the inability to relate one system to
another – comes from the analysis of Building America prototype homes that are 30%
more energy efficient than the Building America Benchmark home standard, as evaluated
against the alternative standards examined in this study.
2
BA 30% Prototype: 2-Story, 2040 ft , Slab Homes
% Savings w.r.t. Specified Reference
35%
30%
25%
20%
15%
10%
5%
0%
Miami
Zone 1
Houston
Zone 2
BA (Current)
Charlotte
Zone 3
IECC 2006
St. Louis
Zone 4
Chicago
Zone 5
HERS 2006
St. Paul
Zone 6
Duluth
Zone 7
BA (Revised)
Figure 1 Bar chart showing the Building America “30% Prototype” home evaluated using the
various performance analysis standards that were examined by this study.
Figure 1 above provides one example of why it is not possible to state with certainty how
the 30% better than Benchmark home compares with either the IECC or with HERS or
even with a hypothetical revised Building America standard [BA (Revised)]. One can
calculate the HERS Index for these homes from the yellow bars as 1-the % savings. They
illustrate that the HERS Index for the homes range from 87 in Duluth (not meeting
ENERGY STAR standard, which requires a HERS Index of 80 or lower in cold climates) to
69 in Charlotte, which is significantly better than ENERGY STAR and, as a matter of fact,
which qualifies for the $2,000 tax credit!
FSEC-CR-1650-06
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While the BA (Current) standards are very consistent at 30% savings across all climate
zones, as Figure 1 shows, there simply is no correlation between that BA figure of merit
and any of the other figures of merit evaluated by this study.
This study provides additional examples of differences among the standards that are
equally disparate. For example, Section 3.3 of the report highlights differences among
the standards for number of stories, foundation type, fuel type and home size that
illustrate that BA % savings can not be well correlated to the HERS Index, even within
the same climate.
It is difficult to make recommendations based on this analysis. There can be pros and
cons for any given methods used to project energy savings. For example, the BA method
was originally developed to measure progress toward a set of U.S. DOE energy savings
milestones called Joules. The intent was to have a consistent standard of performance
tied to mid 1990’s era home standards. However, in the mid 1990’s there were no
definitive code standards for windows that are analogous to those that became effective
in 1998. In addition, there were no standards or methods in the mid 1990’s for the
evaluation of distribution system efficiency, mechanical ventilation or lighting and
appliances in homes.
Since the original objective of this study – to establish a correlation between the BA %
savings value and the HERS Index value – could not be accomplished, there appear to be
three potential options for moving forward. While options may not be considered
recommendations in the conventional sense of the term, they, along with their advantages
and disadvantages, are presented below:
I. Maintain the current BA rule set. This option allows BA program milestones to
continue to be measured from a constant reference point. While this reference point
can not be directly correlated to current codes or to the HERS Index, it does allow
program goals to remain consistent with past objectives. However, this advantage
also works as a disadvantage. Potential builder partners can not be told with
certainty how much better than code their homes will be as the savings with respect
to minimum code standards varies greatly with climate. Thus, builder partners are
left in a bit of a quandary as to how they can advertise these homes in a way that
can be simply explained to their potential customers.
II. Revise the BA rule set. While revising the BA rule set may bring it more in line
with alternative, more current rule sets, the analysis presented here did not show
that this would result in a complete correlation between the revised BA % savings
values and the HERS Index (or Code e-Ratio). The revised BA rule set examined
here consistently resulted in lower % savings values than the HERS rule set. Thus,
adopting the revised BA rule set used in this analysis would cause the BA program
goals to appear significantly more difficult than code-based programs.
III. Migrate to the HERS Index. A large disadvantage of migrating to the HERS Index
is that it would change the basis of BA program savings goals and milestones. Of
FSEC-CR-1650-06
3
course, the previous option, revising the BA rule set, would do the same. There are,
however, some advantages of this option. The HERS Index is widely used as a
performance metric. It is used as the basis for the ENERGY STAR new homes
program and other emerging national programs like USGBC’s pilot LEED-H
program. The HERS rule set also forms the basis for the EPAct 2005 federal tax
credit for highly efficient new homes.
As a metric, the HERS Index includes all of the energy uses of a home. This is one
of the basic tenets of the BA program – that whole home energy use forms the basis
of the program. While changing the BA program standard to the IECC rule set
would violate this tenet, changing to the HERS rule set standard would not. The
HERS rule set a methodology to “score” the use of on-site energy production,
whether by solar, wind or other “free” fuel resources or by highly efficient on-site
conventional fuel technologies like micro-turbines and small combined heat and
power plants. A significant advantage of the HERS rule set standard is that it is a
consensus-based national standard.
A disadvantage of the HERS Index is that the “scoring method” used by the rule set
does not use energy use as the metric. The metric used by the HERS rule set is
called the normalized modified loads method. 1 It was derived as a compromise
consensus method of avoiding the fight between site energy use and source energy
use. It can be shown to reasonably reflect energy cost in a market where the ratio
between site costs for electricity and natural gas are near the ratio of 3 to 1.
Finally, one advantage of using the HERS Index is that it can be explained fairly
simply – the “American Standard New Home” has an index of 100 and a home that
uses no purchased energy has an index of 0. In other words, zero is zero and
anything greater than 100 probably doesn’t meet current minimum energy
standards.
1
Fairey, P., J. Tait, D. Goldstein, D. Tracey, M. Holtz, and R. Judkoff, "The HERS Rating Method and the
Derivation of the Normalized Modified Loads Method." Research Report No. FSEC-RR-54-00, Florida
Solar Energy Center, Cocoa, FL, October 11, 2000.
FSEC-CR-1650-06
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1
INTRODUCTION
1.1
Background
The U.S. Department of Energy’s (DOE) Building America (www.buildingamerica.gov)
has adopted the theme “Research Toward Zero Energy Homes.” As part of the process of
achieving this long-term goal, DOE’s Building America team members evaluate their
progress using the Building America Benchmarking Analysis process. 2 This process is
based on a comparative analysis procedure developed by the National Renewable Energy
Laboratory (NREL) in collaboration with the U.S. DOE and their Building America
research team members. The current analysis method is approximately based on the 1993
Model Energy Code (MEC 93) as the performance basis for comparison and was adopted
and published by NREL in December 2004 (see footnote 1).
During the 13 years since MEC 93 was promulgated, model energy codes have
undergone numerous changes, including changing their moniker to the International
Energy Conservation Code (IECC). The most recent promulgation of the IECC is the
2006 version. In addition, in late 2005, the Residential Energy Services Network, Inc.
(RESNET) adopted and promulgated revised standards for Home Energy Rating Systems
(HERS). 3 Both the IECC and RESNET have updated their standards to become more or
less aligned with each other and to reflect current market products and building practices.
In September of 2005, the U.S. Congress passed the Energy Policy Act of 2005
(EPAct 2005), which contained tax credit provisions for new, highly-efficient homes.
The standards used for determining qualification for this new home tax credit are the
same as the standards used by RESNET accredited programs for the determination of
HERS ratings.
1.2
Objectives
The U.S. DOE, their contractors and research team members have questioned how the
above standards, which are currently used in different realms for comparative analysis of
building energy efficiency performance, are related to one another. The objective of this
study is to provide the analysis needed to help answer this question. The stated tasks to
accomplish this objective are as follows:
1. Compare the Building America (BA) 30% and 50% goals with the 2006
“expanded” whole-house HERS Index.
2. Determine the performance of IECC 2006 minimum code Standard Reference
Design homes relative to the BA Benchmark Home.
3. Analyze the 2006 ENERGY STAR® reference home to determine the level at which
BA prototype homes meet the ENERGY STAR homes criteria.
2
See http://www.eere.energy.gov/buildings/building_america/pa_resources.html
2006 Mortgage Industry Notional Home Energy Rating Systems Standards, Residential Energy Services
Network, Oceanside, CA, August 21, 2006.
3
FSEC-CR-1650-06
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2
METHODS
2.1
Home Selection
The process of creating a set of building simulation files with their respective envelope
components that is representative of Building America (BA) prototype construction
practices can be a complex one. The % of new housing starts by BA climate zones
(Figure 2.1) complicates it further. During the beginning of the study, four sources of
data were searched in an attempt to simplify the process. These sources of building
construction data are as follows:
•
•
•
•
The Building America data base under the DOE-EERE Buildings
Technologies Program
(http://www.eere.energy.gov/buildings/building_america/)
U.S. Census Bureau internet site. (http://www.census.gov/)
Energy Gauge (FL) and Energy Gauge USA database files at FSEC
Sample of EGUSA files (.enb) submitted by other BA teams
Top 50 Permit Areas
Breakdown by Climate Zone
Mixed-Dry
Marine
0%
6%
MixedCold
Mixed-Humid
Humid
18%
32%
Hot Dry
Hot -humid
Cold
Marine
Mixed-Dry
Hot -humid
Hot Dry
30%
14%
Figure 2.1 Percentage of Top 50 construction cities by climate zones ending on June
2005
The BA database under the DOE-EERE Buildings Technologies Program website was
searched to help determine building parameters such as average home size and equipment
efficiency among other variables. Although the database is easy to navigate and
informative, we found that it could not provide all of the statistics and building envelope
variables needed for the project. The Energy Gauge residential building database at the
FSEC-CR-1650-06
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Florida Solar Energy Center (FSEC) was also utilized due to its unlimited query options.
However, a majority of the records found mostly apply to Hot-Humid climate and are not
representative of BA building practices in other climate zones. Prototype building files
submitted by three other BA teams were also scrutinized, which help identify current
building envelope measures being used on BA single-family homes. These 18
benchmark building cases covered all climate zones except for the Marine climate.
To simplify the building file creation process, data sources such as the U.S. Census
Bureau, provided information that can be related to building sizes utilized. For example,
Figure 2.2 presents a breakdown of completed single-family homes by size. The range of
home sizes used throughout this report was further reduced by generating three building
size cases (1200 ft2, 2000 ft2, and 3000 ft2) those of which fall within the boundaries of
the ranges shown on the plot.
Other statistical data plots generated from data found at the Bureau of Census which are
representative of current building construction can be found in appendix B of this report.
Charts related to square footage by region, number of stories, foundation, wall envelope
and heating fuel type are included in the appendix.
2004, 2000 & 1990 Single-Family Homes
Completed Homes (000s)
350
300
2000
250
3000
2004
1200
200
1990
2000
150
100
50
0
<1200
1200-1599 1600-1999 2000-2399 2400-2999
>3000
Square Feet of Floor Area (Sq. ft.)
Figure 2.2 Breakdown of sizes for single family homes completed
2.2
Performance Comparison
2.2.1
Comparative Analysis Rule Sets
A “rule set” is a set of specific instructions as to how a comparative building energy
analysis is to be performed. In general, comparative building energy analysis procedures
require 3 different building configurations, as follows:
FSEC-CR-1650-06
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1. Actual Home: This is the building exactly as it is planned to be built or as it is
actually built.
2. Evaluated Home: This is the Actual Home with specific changes that are required
by the rule set. Usually such changes are specified by the rule set in order to
eliminate lifestyle influences from the building analysis. For example, the Actual
Home may have a thermostat setting of 75 oF year around but the rule set may
require that the Evaluated Home have thermostat settings of 78 oF and 68 oF for
cooling and heating respectively.
3. Reference Home: This home is normally a “geometric twin” of the Actual and
Evaluated Homes that is configured to have envelope and equipment energy
features that are equal to some standard such as a national energy code.
It is important to recognize that different comparative evaluation systems have chosen
different names for these three buildings. For example, the BA comparative analysis
procedure refers the Evaluated Home as the “Prototype” and the Reference Homes as the
“Benchmark.” Likewise, the IECC procedure refers to the Evaluated Home as the
“Proposed Design” and the Reference Home as the “Standard Reference Design” and the
HERS procedure refers to the Evaluated Home as the “Rated Home” and the Reference
Home as the “HERS Reference Home.”
For the purposes of this document, and from this point forward, the terms Actual Home,
Evaluated Home and Reference Home will be used to refer to these three buildings in
order to ensure consistency of meaning throughout this document.
2.2.2
Rule Set Differences
There are a number of major differences between the Building America (BA)
Benchmarking rule set and the 2006 HERS and 2006 IECC rule sets. They may be
summarized as follows:
•
Thermostats: The BA rule set requires that thermostats in both the Evaluated
Home and the Reference Home be set to 76 for cooling and 71 for heating. The
HERS and IECC rules sets require that they be set to 78 for cooling and 68 for
heating in the Evaluated Home and the Reference Home.
•
Windows: The BA rule set uses Reference Home window characteristics that are
considered typical of 1993 practice. This is prior to the IECC separating window
and wall U-factors and establishing minimum standards for window SHGC,
which occurred in 1998. As a result, the BA rule set for windows in the
Reference Home are substantially different from the HERS and IECC rule sets for
windows in the Reference Home.
•
Infiltration and mechanical ventilation: The BA rule set uses a Reference Home
specific leakage area (SLA=0.00057) that is 18.75% greater than the HERS rules
set (SLA = 0.00048) and 58.3% greater than the IECC rule set (SLA = 0.00036).
FSEC-CR-1650-06
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Mechanical ventilation is also treated substantially different between the different
rule sets. For the BA rule set, both the Reference Home and the Evaluated Home
are required to incorporate mechanical ventilation, with the Reference Home
required to have balanced mechanical ventilation meeting ASHRAE 62.2
Standards. For the HERS and IECC rule sets, there is no requirement for
mechanical ventilation, however, where mechanical ventilation is present in the
Actual Home, it is incorporated in the Evaluated Home at the ASHRAE 62.2
minimum ventilation rate.
However, the HERS and IECC Reference Homes are treated differently than the
BA Reference Home. In both the HERS and IECC rule sets, the Reference Home
does not have increased air exchange over and above the natural infiltration air
exchange resulting from the Reference Home SLA requirement. To account for
the fact that mechanical ventilation in the Evaluated Home will result in an
increase in fan energy compared with no mechanical ventilation, the Reference
Homes for the HERS and IECC rule sets have an added fan energy use that is
equivalent to a mechanical ventilation fan energy use of 0.45 watts/cfm of air
flow. The BA Reference Home uses the same additional fan energy for
mechanical ventilation.
Unlike the HERS and IECC rule set requirements, the BA Reference Home rule
set requires that the minimum ASHRAE 62.2 mechanical ventilation be provided
to the Reference Home through a balanced mechanical system, which supplies
and exhausts the same amount of air mechanically. This requirement is in
addition to the infiltration resulting from SLA = 0.00057 for the BA Reference
Home. This means the ventilation air is added to the infiltration air in the BA
Reference Home as straight addition, rather than in quadrature, as would be the
case for unbalanced mechanical ventilation.
The result of these differences in the treatment of infiltration and mechanical
ventilation can be significant. For example, for a 2040 square foot, 2-story, 3bedroom home, located in Chicago, IL, the BA Reference Home would have an
overall air exchange rate (infiltration + mechanical ventilation) of 0.82 air
changes per hour (ach). However, the same home, when configured according to
the HERS and IECC Reference Home rule sets would have overall air exchange
rates of 0.55 and 0.41 ach, respectively. In very cold climates, these differences
in Reference Home air exchange rates can result in substantial differences in the
comparative results.
•
Distribution System Efficiency (DSE). The BA Reference Home distribution
system efficiency rule set differs from the HERS and IECC Reference Home rule
sets. For HERS and IECC the DSE for the Reference Home is characterized by a
single value (DSE=0.80), regardless of home type. However, for the BA
Reference Home, the efficiency of the distribution system is dependent on the
foundation type and number of stories of the Actual Home. For example, if the
Actual Home is a one-story, slab on grade home, the BA Reference Home duct
FSEC-CR-1650-06
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system is specified to be 100% in the attic of the home and to have air leakage to
outdoors equal to 15% of the AHU fan flow. However, if the Actual Home is a
two-story, slab on grade home, then the BA Reference Home duct system is
specified to be 35% in the conditioned space and 65% in the attic and to have air
leakage to the outdoors of 15% * 65% = 9.75% of the AHU fan flow.
•
NAECA Equipment Standards. The BA rule set specifies Reference Home
equipment efficiencies that are different than the current NAECA minimum
standards. The BA rule set specifies equipment efficiencies that predate the 2004
NAECA water heater efficiency modifications and the 2006 air conditioning and
heating system modifications. On the other hand, both the HERS and IECC rule
sets specify that the “prevailing federal minimum standard” equipment
efficiencies be used for the Reference Home.
•
Water Heating. The number of gallons per day (gpd) for water heating is
dependent only on the number of bedrooms for the IECC and HERS rule sets but
is dependent on other additional factors for the BA rule set.
In addition to the above there are significant differences between the treatment of internal
gains in the BA rule set and the HERS and IECC rule sets. The HERS and IECC rule
sets call for the application of internal gains that are a function of only the conditioned
square footage and the number of bedrooms of the home [iGain = 17,900 + 23.8 * CFA +
4104 * Nbr (Btu/day per dwelling unit)]. The BA rule set calls for the application of
internal gains which vary by the location of the home, with location multipliers for the
miscellaneous electrical uses that range from a low of 0.77 to a high of 1.11.
Additionally, the BA rule set treats internal gains in homes with gas devices differently
than all electric homes, with greater internal gains in gas homes.
2.3
General Analysis Methods
The first step of the analysis process was to select a representative set of proposed BA
home plans and specification for small, medium and large homes. For the most part,
homes were selected from actual builder models. The medium sized home is used as the
basis for much of the analysis. Significant care was taken to create both a 2-story and a
1-story medium sized model, having the same conditioned square footage, with the same
envelope and equipment characteristics, the same window-to-floor-area ratio and the
same window orientation percentages so that differences in these characteristics would
not confound the analysis of the impact of the number of stories.
A total of seven climate locations were selected for the analysis as shown in Figure 2.3,
below. One TMY city was selected from each of the IECC climate zones for the
contiguous U.S.
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Figure 2.3 IECC Climate map showing the TMY cities selected for the analysis using each of
the 7 climate zones within the contiguous U.S.
Once the set of BA homes was selected, the BA Benchmark spreadsheet tool developed
by NREL 4 and modified by FSEC was used to determine the appropriate EnergyGauge
USA modeling inputs for the benchmark and the prototype homes using the Actual
Homes as the basis.
Using EnergyGauge modeling results, the Actual and Evaluated Homes were iteratively
adjusted such that the Benchmark spreadsheet tool yielded output results showing BA
whole-building energy savings as close to 30% as reasonably possible. Results of this
process are presented in detail in Table 2.1 on the following 2 pages.
4
Building America Analysis Spreadsheet, dated 05.03/06 found online at
http://www.eere.energy.gov/buildings/building_america/pa_resources.html
FSEC-CR-1650-06
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Table 2.1 Characteristics of the 30% BA Prototype homes used as the basis for the majority of the analysis
(yellow highlighting represents properties that differ).
Climate Location:
Envelope Characteristics:
Conditioned floor area (ft2)
no. stories
no. bedrooms
avg. ceiling height (ft)
attached garage
foundation type
slab area (ft2)
slab insulation
slab perimeter (ft)
roof type
roof pitch
roof cover
roof color
roof solar absorptance
roof insulation
attic type
attic ventilation
ceiling type
ceiling area (ft2)
ceiling insulation
wall type
wall insulation
Sheathing R-value
wall solar absorptance
door type
door area (ft2)
window type
size (% CFA)
orientation
U-Factor
SHGC
FSEC-CR-1650-06
Miami, FL
Houston, TX
Charlotte, NC
St. Louis, MO
Chicago, IL
St. Paul, MN
Duluth, MN
2040
2
3
9
yes
slab on grade
870
none
180
hip
5:12
comp shingles
Dark
0.92
none
standard
1:300
flat
1170
R-19.0
Frame-wood
R-11.0
none
0.75
insulated
40
double, low-e
16.6%
~40% E & W
~10% N & S
0.57
0.45
2040
2
3
9
yes
slab on grade
870
none
180
hip
5:12
comp shingles
Dark
0.92
none
standard
1:300
flat
1170
R-30.0
Frame-wood
R-13.0
3.75
0.75
insulated
40
double, low-e
16.6%
~40% E & W
~10% N & S
0.39
0.28
2040
2
3
9
yes
slab on grade
870
R-4.0
180
hip
5:12
comp shingles
Dark
0.92
none
standard
1:300
flat
1170
R-36.0
Frame-wood
R-22
3.1
0.75
insulated
40
double, low-e
16.6%
~40% E & W
~10% N & S
0.3
0.5
2040
2
3
9
yes
slab on grade
870
R-4.0
180
hip
5:12
comp shingles
Dark
0.92
none
standard
1:300
flat
1170
R-34.0
Frame-wood
R-20.0
none
0.75
insulated
40
double, low-e
16.6%
~40% E & W
~10% N & S
0.4
0.5
2040
2
3
9
yes
slab on grade
870
R-5.35
180
hip
5:12
comp shingles
Dark
0.92
none
standard
1:300
flat
1170
R-40
Frame-wood
R-21.0
3.75
0.75
insulated
40
double, low-e
16.6%
~40% E & W
~10% N & S
0.35
0.55
2040
2
3
9
yes
slab on grade
870
R-6.32
180
hip
5:12
comp shingles
Dark
0.92
none
standard
1:300
flat
1170
R-38
Frame-wood
R-19
none
0.75
insulated
40
double, low-e
16.6%
~40% E & W
~10% N & S
0.35
0.55
2040
2
3
9
yes
slab on grade
870
R-6.32
180
hip
5:12
comp shingles
Dark
0.92
none
standard
1:300
flat
1170
R-30
Frame-wood
R-19
none
0.75
insulated
40
double, low-e
16.6%
~40% E & W
~10% N & S
0.35
0.4
12
Climate Location:
Overhang (ft)
envelope leakage
leakage rate (ach50)
Mechanical ventilation
Supply vent rate (cfm)
Systems:
cooling type
cooling SEER
heating type
heating HSPF
thermostat schedule
setpoint (htng/cool) (oF)
distribution system
duct insulation
duct location
AHU location
duct leakage
return leak fraction
hot water type (gal - fuel)
auxiliary elec. EF
Lighting & appliances:
% fluorescent
eStar refrigerator
eStar dishwasher
eStar ceiling fans
Dryer
Range
FSEC-CR-1650-06
Miami, FL
1.5
standard
4
unbalanced
50.4
Houston, TX
1.5
standard
4
unbalanced
50.4
Charlotte, NC
1.5
standard
4
unbalanced
50.4
St. Louis, MO
1.5
standard
4
unbalanced
50.4
Chicago, IL
1.5
standard
4
unbalanced
50.4
St. Paul, MN
1.5
standard
4
unbalanced
50.4
Duluth, MN
1.5
standard
4
unbalanced
50.4
central
14
Heat Pump
8.2
BA Bench
71/76
forced air
R-6
Attic
Interior
Qn = 0.04
0.33
50 - electric
0.9
central
14
Heat Pump
8.2
BA Bench
71/76
forced air
R-6
Attic
Interior
Qn = 0.04
0.33
50 - electric
0.9
central
14
Heat Pump
8.2
BA Bench
71/76
forced air
R-6
Attic
Interior
Qn = 0.04
0.33
50 - electric
0.9
central
14
Heat Pump
8.2
BA Bench
71/76
forced air
R-6
Attic
Interior
Qn = 0.04
0.33
50 - electric
0.9
central
14
Heat Pump
8.2
BA Bench
71/76
forced air
R-6
Attic
Interior
Qn = 0.04
0.33
50 - electric
0.9
central
13
Heat Pump
8.2
BA Bench
71/76
forced air
R-6
Attic
Interior
Qn = 0.04
0.33
50 - electric
0.9
central
13
Heat Pump
8.2
BA Bench
71/76
forced air
R-6
Attic
Interior
Qn = 0.04
0.33
50 - electric
0.9
50%
no
no
no
electric
electric
50%
no
no
no
electric
electric
50%
no
no
no
electric
electric
50%
no
no
no
electric
electric
50%
no
no
n0
electric
electric
50%
no
no
n0
electric
electric
50%
no
no
no
electric
electric
13
2.3.1
BA Rule Set as the Basis for Analysis
The process of accomplishing the analysis using consistent assumptions is complicated
by the differences in rule sets that are described above. In general, the BA rule set served
as the basis for the analysis and the following assumptions were maintained for the
simulations:
•
All homes were modeled including mechanical ventilation. For the BA Reference
Home, mechanical ventilation is specified by the benchmark analysis procedures
as being balanced flow in accordance with ASHRAE Standard 62.2. For
Evaluated Homes, the same amount of mechanical ventilation is also used
however, the flow is assumed to be unbalanced (supply-only ventilation). This is
true even for the cases that are designed to represent the alternative Reference
Homes (i.e. HERS and IECC), where mechanical ventilation is added to those
Reference Homes for the purpose of comparing with the BA Reference Home.
Where the Actual and Evaluated Homes are configured as the Reference Home in
accordance with the HERS and IECC rule sets, this additional mechanical
ventilation is provided as unbalanced, supply-only mechanical ventilation that is
in addition to the required SLA for the respective Reference Home. Thus, for
configurations corresponding with the HERS Reference Home, the SLA is
0.00048 and for configurations corresponding with the IECC Reference Home,
the SLA is 0.00036.
These additional mechanical ventilation assumptions, which are not required for
Reference Homes by either the IECC or HERS rule sets, result in slightly
increased energy use in homes that are otherwise configured as HERS and IECC
Reference Homes. As a result, cases designated as IECC Standard Design and
HERS Reference configurations will not necessarily have the same energy use as
the actual IECC or HERS Reference Homes and will result in HERS Indexes
slightly greater than 100 and IECC e-Ratios slightly greater than 1.00.
•
All homes were modeled using the BA thermostat schedule. Since the BA rule
set requires a different thermostat schedule from the other reference home rule
sets, the BA thermostat schedule is incorporated into the alternative Reference
Home cases for the purpose of comparing the BA Reference Homes with the
alternative Reference Homes. It is important to note that identical thermostat
settings are used in both the Reference Home and the Evaluated Home in all
cases, whether they are from the BA rule set or an alternative rule set.
•
All homes were modeled using the BA hot water heater gallons per day (gpd).
For the BA Reference Home, the daily hot water use is dependent on both the
number of occupants and the temperature of the inlet water. This results in hot
water use (gpd) that varies by climate. For the purpose of comparing the BA
Reference Home with the alternative Reference Homes, the hot water use was
altered in the alternative Reference Homes to match the BA requirement.
FSEC-CR-1650-06
14
•
2.3.2
Miscellaneous Energy Consumption is as specified by BA Benchmark. While
EnergyGauge automatically generates miscellaneous energy uses in accordance
with IECC and HERS Standards, these values are different from the values used
in the BA benchmarking analysis procedures. For the purposes of the
comparisons presented in this report, only the heating, cooling and hot water
energy use results are taken from EnergyGauge results. The remaining energy
uses for the homes are as calculated by the Building America Analysis
Spreadsheet (see footnote 1, above).
Additional Modeling Assumptions for Evaluated Homes
In addition to the above assumptions, which are related primarily to the BA rule set
requirements, there are some additional assumptions regarding modeling of the Evaluated
Homes in the analysis reported here.
•
Windows Orientation. The home plans selected for the Actual Homes in this
analysis, were oriented so as to produce the worst case results for the Homes. For
example, the 2040 ft2 homes have a large fraction of their windows on the front
and back of the home and only a very small fraction on the sides. The Evaluated
Home orientation used for analysis of these homes was with the front of the home
facing west and the back facing east, resulting in a “worst case” simulation result.
•
Window Area. The Actual and Evaluated Homes generally have less window
area than the Reference Homes. For example, the 2040 ft2 homes have a window
to floor area ratio of 16.6% rather than the 18% ratio that is used for the BA and
HERS Reference Home standards. However, for the IECC Reference Home, the
window to floor area ratio is required to be equal to that of the Actual Home
unless the Actual Home ratio greater than 18%, above which point the IECC
Reference Home is required to maintain a window to floor area ratio of 18%.
These window area assumptions produce modest differences between the HERS
and IECC results due to the fact that the HERS rule set results in some credit for
the reduced window area in the Actual Home as compared with the Reference
Home. On the other hand the IECC rule set requires that the IECC Reference
Home have the same window to floor area ratio as the Actual Home for this case.
•
Thermostats. It is important to note that thermostat schedules in the Evaluated
Home are always maintained at the same settings as for the Reference Home in all
cases.
2.3.3
HERS and IECC Figures of Merit
When determining a HERS Index or an IECC Code Compliance figure of merit for
homes, the items listed in Section 2.3.1 are treated in accordance with the rule set for the
appropriate standard (i.e. either HERS or IECC) rather than as described above. For
these purposes, mechanical ventilation fan power in the homes is set to 0.4 watts/cfm of
FSEC-CR-1650-06
15
ventilation airflow. This is done so that the HERS and IECC savings are not exaggerated
as would otherwise be the case if the fan power were left at 0 as is required by BA
procedures for simulations where results are for use in the BA spreadsheet analysis,
where mechanical ventilation fan power is added separately through the spreadsheet.
The EnergyGauge figure of merit for IECC Code compliance is called the e-Ratio, which
is the result of dividing the total projected energy use for heating, cooling and hot water
in the Evaluated Home by the total projected energy use for heating, cooling and hot
water in the Reference Home. Thus, like the HERS Index, the smaller the value, the
more efficient the home. The e-Ratio, when multiplied by 100, is a very similar figure of
merit to the HERS Index, except that it does not consider energy uses other than the code
energy uses of heating, cooling and hot water.
FSEC-CR-1650-06
16
3
RESULTS
3.1
Revised Benchmark Incremental Analysis
As part of the analysis, the major differences between the BA rule set and the HERS and
IECC rule sets described in Section 2.2.2 were examined on both an individual and a
cumulative basis. This was accomplished by revising, one-by-one, the BA Reference
Home characteristics to those of the HERS Reference Home for each of the major items
that differ, as provided in Table 3.1, below:
Table 3.1 Characteristic Substitutions for Revised Benchmark Analysis
BA Reference Home
Current BA Reference
Revised BA Reference
Characteristic
Value or Setting
Value or Setting
o
o
Thermostat Setting
Cool = 76 F; Heat = 71 F
Cool = 78 oF; Heat = 68 oF
Heating, Cooling and Hot HSPF = 6.8; SEER = 10;
HSPF = 7.7; SEER = 13;
Water Equipment
EF = 0.86
EF = 0.90
Windows: (Miami)
U=1.00; SHGC=0.79
U=1.20; SHGC=0.40
(Houston)
U=0.79; SHGC=0.65
U=0.75; SHGC=0.40
(Charlotte)
U=0.58; SHGC=0.58
U=0.65; SHGC=0.40
(St. Louis)
U=0.53; SHGC=0.58
U=0.40; SHGC=0.55
(Chicago)
U=0.39; SHGC=0.32
U=0.35; SHGC=0.55
(St. Paul)
U=0.36; SHGC=0.32
U=0.35; SHGC=0.55
(Duluth)
U=0.36; SHGC=0.32
U=0.35; SHGC=0.55
Distribution System
1-story, slab: 100% ducts in DSE = 0.80
Efficiency (DSE)
attic; 15% air leakage
2-story, slab: 65% ducts in
DSE = 0.80
attic; 9.75% air leakage
2-story, crawlspace: 65%
DSE = 0.80
ducts in crawl; 9.75% air
leakage
DSE = 0.80
Basement: 100% ducts in
conditioned basement; no
air leakage
Envelope Leakage*
1-story: SLA = 0.00057
SLA = 0.00048
SLA = 0.00048
2-story: SLA = 0.00046
Mechanical Ventilation*
Balanced system
Unbalanced, supply only**
* Leakage and Mech. Vent treated together as a single “Infiltration” characteristic
** Mechanical ventilation air flow is not actually included in HERS Reference Home
It is also important to point out that for thermostat schedules, identical schedules are used
in both the Reference and Evaluated Homes, whether they are the original or the revised
schedule. Finally, following the incremental changes, all of the above items were
cumulatively changed within a single simulation to represent a “Revised” BA Reference
Home containing all of the differences.
FSEC-CR-1650-06
17
Results from the above analysis are quite informative as to the individual contribution of
each difference to the total cumulative difference as well as to indicate how climate,
foundation type, number of stories and fuel type impact both the individual differences
and the cumulative differences. Figure 3.1 below provides an example of results from
such an analysis for Chicago, Illinois. Some explanation is helpful. The results are for
“30% BA Prototype” homes as compared against the various Reference Home conditions
shown by the x-axis labels. With the exception of the BA rules for foundation type and
number of stories, the characteristics of the 30% BA Prototype homes are the same for all
cases. The 2-story slab-on-grade case is the “calibration” case, which is used to determine
the envelope and equipment characteristics for the 30% BA Prototype. These same
envelope and equipment characteristics are then used for all other prototype cases so that
all the 30% BA Prototypes have identical envelope and equipment characteristics.
2
Incremental Analysis: 2040 ft , Chicago Homes
Savings w.r.t. Revised BA Reference (%)
35%
30%
25%
20%
15%
10%
5%
0%
Current
Distribution
2-Story, Slab
Thermostat
Equipment
1-Story, Slab
Windows
Infiltration
2-Story, Crawl
All (Revised)
1-Story, Bsmt
2
Figure 3.1 Bar chart of “Revised Benchmark” savings for 2040 ft “30% BA Prototype”
homes in Chicago, Illinois, using “revised” BA Reference Homes and showing the impact of
foundation type and number of stories. The first group of bars [Current] shows the homes
evaluated using the current BA Reference Home characteristics with succeeding groups
representing individual revisions to this Reference Home and the final bar group [All
(Revised)] corresponding to all of the characteristics being changed for the Reference Home.
The Evaluated Home (30% BA Prototype) characteristics are not altered in this analysis,
excepting for the Thermostat runs where the thermostat is revised in both the Reference and
Evaluated Homes, where it produces about a 2% decrease is savings for all homes.
While the crawlspace home tracks the 2-story, slab home rather closely, some significant
differences do occur for the other two homes in Figure 3.1. For the 1-story home, the %
savings predicted using the current BA reference characteristics are significantly greater
FSEC-CR-1650-06
18
than for the 2-story home. Note that this advantage is more than eliminated when the
distribution system efficiency is changed to that of the HERS rule set. Also note that
when all revisions are included in the Reference Home, this foundation type shows the
lowest savings of all the cases shown.
The basement home is also interesting. This home has two floors; one is a conditioned,
finished walkout basement with half of its wall area below ground, and the second is
directly above the basement. This home had its basement window area reduced by 50%
compared to the 1st story of the 2-story prototype so as to equitably correspond with the
BA rule set for basement Reference Homes. Again, note what happens when the
distribution system efficiency is changed to that of the HERS rule set – the % savings for
this case increases dramatically. This fairly dramatic impact also shows up in the final
accumulation of the differences with this home showing the greatest % savings when all
the revisions are included in the BA Reference Home.
Climate effects can also be examined using this incremental analysis technique. Figure
3.2, below shows how the individual differences in three climates (one cooling
dominated, one mixed and one cold) combine to lead to very different combined results.
2
Incremental Analysis: 2-Story, 2040 ft , Slab-on-Grade Homes
Savings w.r.t. Revised BA Reference (%)
35%
30%
25%
20%
15%
10%
5%
0%
Current
Distribution Thermostat
Miami
Equipment
Charlotte
Windows
Infiltration
All (Revised)
Duluth
Figure 3.2 Bar chart of “Revised Benchmark” savings for 2-Story, 2040 ft2, slab-on-grade
“30% BA Prototype” homes in cooling dominated, mixed, and heating dominated climates,
showing the climatic impacts of revisions to the BA Reference Home characteristics.
It is clear from Figure 3.2 that equipment efficiency and window characteristic changes
result in large differences in Miami, where cooling dominates the energy needs. For
FSEC-CR-1650-06
19
Duluth, window differences are also important but infiltration ventilation and distribution
system differences cause the largest changes. Charlotte, on the other hand, suffers from
the fact that the Current BA window characteristics are more stringent than the 2006
HERS and IECC window characteristics, such that BA 30% Prototype savings increase
when the Reference Home is changed to incorporate the 2006 window characteristics.
Finally, Figure 3.3, below, provides summary data for a revised BA Reference Home rule
set across all of the 7 climate zones evaluated. It is clear from Figure 3.3 that there are
significant climatic differences between the current BA rule set and any revised BA rule
set that might be adopted to reduce the differences between BA evaluations and
evaluations conducted using current HERS (or IECC) rule sets. Based on these results,
there does not appear to be any consistent correlation, which could be used across
climates zones, to establish any relationship between BA and HERS (or IECC) projected
savings results. In other words, the data show that we can not say what HERS Index is
equivalent to the BA 30% Prototype. The HERS Indices for these BA 30% Prototype
cases range from a high of 87 in Duluth to a low of 68 in Charlotte.
2
BA 30% Prototype: 2-Story, 2040 ft , Slab Homes
% Savings w.r.t. Specified Reference
35%
30%
25%
20%
15%
10%
5%
0%
Miami
Zone 1
Houston
Zone 2
BA (Current)
Charlotte
Zone 3
St. Louis
Zone 4
HERS 2006
Chicago
Zone 5
St. Paul
Zone 6
Duluth
Zone 7
BA (Revised)
Figure 3.3 Bar chart showing the relationship between the current BA rules set, the HERS
2006 rule set and a fully-revised BA rule set that incorporates all major differences between the
current BA rule set and the 2006 HERS rule set.
3.2
Comparisons of BA, HERS and IECC Reference Standards
Another way to look at overall differences between the BA, HERS and IECC rule sets is
to compare the % savings results for the 30% BA Prototype against the % savings results
FSEC-CR-1650-06
20
for the same home when it is configured to match the Reference Home characteristics of
alternative standards. In the previous analysis, the Reference Home characteristics were
changed while the Evaluated Home characteristics remained constant. In this analysis, we
do the opposite and the characteristics of the Evaluated Home are changed while the
Reference Home characteristics remain constant.
3.2.1
Comparisons of the Reference Home Standards
While the previous comparison shows how predicted savings would change if the
Reference for the 30% BA Prototype is changed, this analysis shows the energy
efficiency of the alternative Reference Homes with respect to the BA Reference Home.
2
Various References: 2-Story, 2040 ft , Slab-on-Grade Home
28%
27%
% Savings w.r.t. BA Reference Home
26%
24%
24%
23%
21%
22%
21%
21%
20%
20%
18%
16%
16%
16%
15%
16%
13%
12%
11%
9%
8%
8%
6%
4%
4%
1%
0%
Miami
Zone 1
Houston
Zone 2
IECC 2006
Charlotte
Zone 3
St. Louis
Zone 4
HERS 2006
Chicago
Zone 5
St. Paul
Zone 6
Duluth
Zone 7
HERS 1999
Figure 3.4 Bar chart of the % savings for the 2-Story, 2040ft2, slab-on-grade home configured
to match the characteristics of the IECC and HERS Reference Home rule sets. By definition,
the BA Reference Home would produce 0% savings on this chart, so each of the alternative rule
sets produce Reference Homes that are more energy-efficient than the BA Reference Home.
Figure 3.4 illustrates a number of interesting facts. First, it is clear from the figure how
much more efficient the HERS 2006 standard is compared with the HERS 1999 standard
in the south where we see about 15% difference. Only about half that amount occurs in
the north. Second, in Miami and in the far north (zones 5-7), the 2006 HERS and IECC
Reference Homes are 20-25% more efficient than the BA Reference Home. However, in
mid climate zones (2-4), the 2006 HERS and IECC Reference Home standards are much
closer to the BA Reference Home efficiency, with a 2006 HERS Reference home low of
only 9% more efficient than the BA Reference Home in Charlotte (zone 3).
FSEC-CR-1650-06
21
3.2.2
Comparisons with the 2006 IECC Standard
Yet another way to examine the differences between the BA, HERS and IECC standards
is to start with Evaluation Homes that are configured by BA rules to represent the
Reference Homes of the alternative standards and calculate the savings with respect to
the various Reference Homes. Figure 3.5 makes this comparison for the 2006 IECC
Reference Home (Standard Design) configurations.
2
IECC 2006 Standard Design: 2-Story, 2040 ft Slab-on-Grade
% Savings w.r.t. Specified Reference
32%
28%
24%
27%
26%
24%
23%
21%
20%
18%
16%
13%
12%
8%
4%
2%
1%
4%
3%
5%
4%
4%
0%
-4%
-4%
-4%
-3%
-3%
-3%
-3%
-3%
-8%
Miami
Zone 1
Houston
Zone 2
BA (Current)
Charlotte
Zone 3
St. Louis
Zone 4
HERS 2006
Chicago
Zone 5
St. Paul
Zone 6
Duluth
Zone 7
IECC 2006
Figure 3.5 Bar chart of % savings for the IECC Reference Home under 3 different Reference
Home specifications showing that while significant savings are shown for the current BA rule
set, only small to negative savings are shown with respect to the HERS and IECC rule sets.
Figure 3.5 needs some additional clarification. The BA % savings are calculated using
standard BA rules, however, the HERS 2006 and IECC 2006 savings use the HERS and
IECC rule sets to calculate savings. This means that savings for HERS and IECC are
computed using the HERS and IECC figures of merit (the HERS Index and the IECC eRatio). Thus, the IECC and HERS Evaluated Homes are not configured “strictly” by
IECC and HERS Standards. Where they differ is mechanical ventilation, where neither
the IECC nor the HERS rule sets incorporate mechanical ventilation air flow in their
Reference Homes. For these Evaluated Homes, mechanical ventilation in accordance
with ASHRAE Standard 62.2 specifications, including fan power at 0.4watts/cfm, was
added to the Evaluated Homes in addition to the standard envelope specific leakage area
required by the HERS or IECC rule set for Reference Homes. The result of this added
mechanical ventilation air flow is that the Evaluated Homes are slightly less efficient than
FSEC-CR-1650-06
22
their respective rule sets would normally require. As a result, when compared with the
IECC rule set standard for Reference Homes, the IECC Standard Design homes given in
Figure 3.5 show negative savings where they would normally be expected to show zero
savings.
A second item that should be clarified is the difference between the IECC and the HERS
results. These differences occur for two reasons:
•
The SLA for the IECC Reference Home is 0.00036 and the SLA for the HERS
Reference Home is 0.00048, making the IECC Reference Home more efficient
than the HERS Reference Home, especially in northern climates where the energy
impacts of this envelope leakage area difference is magnified by a much larger
indoor-to-outdoor temperature difference and stronger infiltration driving forces.
•
The IECC Reference Home rule set does not allow the Evaluated Home to
achieve any additional efficiency resulting from reduced window area and, for the
cases presented here, the Evaluated Home has a 16.6% window-to-floor area
ratio. This means that the home would achieve efficiency “credit” based on the
HERS rule set but would not achieve that credits based on the 2006 IECC rule set.
3.2.3
Comparisons with the 2006 ENERGY STAR Standard
A similar comparison can be accomplished with the 2006 ENERGY STAR prescriptive
standards 5 where, rather than the 2006 IECC standard, the 2006 ENERGY STAR Builder
Option Package (BOP) standard is used to construct the Evaluated Home and the savings
from the homes are compared across the various rule sets in the various climate zones.
Figure 3.6 presents results from this analysis.
5
EPA, Energy Star Qualified Homes: National Builder Option Package, U.S.
Environmental Protection Agency, Washington, DC, July 1, 2006. Online at
http://www.energystar.gov/ia/partners/bldrs_lenders_raters/downloads/NatBOPTRK_060206.pdf
FSEC-CR-1650-06
23
2
Energy Star 2006 BOP: 2-Story, 2040 ft , Slab-on-Grade
% Savings w.r.t. Specified Reference
36%
32%
35%
31%
31%
30%
29%
28%
25%
25%
24%
20%
18%
16%
16%
15%
15%
14%
14%
15%
14%
13%
12%
12%
12%
11%
10%
8%
8%
4%
0%
Miami
Zone 1
Houston
Zone 2
BA (Current)
Charlotte
Zone 3
St. Louis
Zone 4
HERS 2006
Chicago
Zone 5
St. Paul
Zone 6
Duluth
Zone 7
IECC 2006
Figure 3.6 Bar chart of % savings for the 2006 ENERGY STAR prescriptive specification under
3 different Reference Home specifications showing that the current BA specification predicts
significant savings (=>25%) for ENERGY STAR homes in all climates.
Figure 3.6 shows that the current BA standard produces predicted energy savings
between 25% and 35%. These same homes, when evaluated against the HERS 2006
standard produce predicted savings of 13% to 18% and when evaluated against 2006
IECC standards produce predicted savings of 9% to 15%.
It is important to point out that the ENERGY STAR home cases maintain the same
mechanical ventilation assumptions that were used in the previous analysis for the IECC
Reference Homes. Additionally, they were evaluated using the same procedure, where
the savings for the HERS 2006 and IECC 2006 were calculated using the assumptions of
those respective rule sets. In other words, the additional mechanical ventilation air flows
contained in the ENERGY STAR Evaluated Homes did not exist in the HERS and IECC
Reference Homes to which they were compared.
3.2.4
The HERS Index
Another question that arises is how do these cases stack up on the HERS Index? The
HERS Index is a relative scoring method with a scale from 0 to infinity. A HERS Index
of 0 represents a home with no net purchased energy use and a HERS Index 100
represents the “American Standard Home.” HERS Indices greater than 100 mean that
the home is less efficient than the HERS Reference Home and Indices of less than 100
mean that the home is more efficient than the HERS Reference Home.
FSEC-CR-1650-06
24
2
135
HERS Indices: 2-Story, 2040 ft , Slab-on-Grade Configurations
130
125
2006 HERS Index
120
115
110
105
100
95
90
85
80
75
70
65
Miami
Zone 1
Houston
Zone 2
BA Reference
Charlotte
Zone 3
St. Louis
Zone 4
IECC Reference
Chicago
Zone 5
St. Paul
Zone 6
Duluth
Zone 7
BA 30% Prototype
Figure 3.7 Bar chart of the HERS Index for various Evaluated Home cases showing a
comparison of the BA Reference Home, the IECC Reference Home and the BA 30% Prototype
Home in 7 climate zones.
Figure 3.7 presents the results of a HERS Index analysis showing the relationship
between the BA Reference Home, the IECC Reference Home and the BA 30% Prototype
Home cases. The green dotted line in the figure shows the performance-based criteria for
the 2006 ENERGY STAR program in the 7 climates. Note also that the BA Reference
Home cases all have HERS Indices well in excess of 100.
Note also the red arrow above the Charlotte BA 30% Prototype case. The HERS Index
for this home is 68, indicating that it saves 31% (100 – 69) with respect to the HERS
Reference Home. When evaluated for tax credit qualification, the heating and cooling
envelope savings for this case are 39% and the energy savings for heating and cooling are
53%, qualifying this home for the EPAct 2005 federal tax credit. No other BA 30%
Prototype case qualifies for this tax credit. In fact, the 30% BA prototype cases in St.
Louis and Duluth would not qualify for ENERGY STAR label using the performance
criteria shown by the green dotted line on the chart.
3.3
Impacts of Other Home Characteristics
A number of additional characteristics are treated differently by the different rule sets
and, therefore, they will also impact the projected energy savings of homes. Among
them are: 1) the number of stories in the home, 2) the foundation type used for the home,
FSEC-CR-1650-06
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3) the fuel type used by the home, 4) the internal gains used for the home, 5) the “other”
energy uses of the home and 6) the size (conditioned floor area) of the home.
3.3.1
Number of Stories
The impacts deriving from the number of stories of the home are primarily related to the
differences in treatment of the distribution system efficiencies in the Reference Home
rule sets. Table 3.1 in Section 3.1 above illustrates these differences. For the BA
Reference Home rule set the efficiency of the distribution system is dependent on the
number of stories in the Actual Home. For example, for single-story, slab-on-grade
homes, 100% of the ducts are assumed to be in the attic in the Reference Home.
Additionally, the Reference Home distribution system is assumed to have air leakage to
outdoors equal to 15% of the rated fan flow of the air handling equipment.
If this same home is converted to a 2-story structure, with the identical conditioned
square footage, window area and other energy characteristics, 65% of the Reference
Home ducts are assumed to be in the attic and 35% in the conditioned space. This same
65%-35% ratio is applied to the distribution system leakage, such that 15% x 65% =
9.75% of the rated fan flow is assumed to be leakage to outdoors in the Reference Home.
These differences in the BA Reference Home result in differences in predicted energy
savings for homes with different numbers of stories but with otherwise identical energy
characteristics.
2
No. of Story Impacts: 2040 ft , Slab-on-Grade, 30% BA Homes
% Savings w.r.t. Specified Reference
40%
35%
35%
32%
30%
30%
30%
25%
24%
23%
21%
20%
18%
17%
15%
15%
14%
11% 11%
9%
10%
6%
5%
3%
0%
Houston
2-Story
BA (Current)
Houston
1-Story
HERS 2006
Chicago
2-Story
IECC 2006
Chicago
1-Story
BA (Revised)
Figure 3.8 Bar chart showing impact of number of stories as a function of the rule set used to
determine the savings.
FSEC-CR-1650-06
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Figure 3.8, above, illustrates how the number of stories of a home impacts the predicted
percentage energy savings as a function of the rule set used to calculate the savings. For
this figure, all Evaluated Home characteristics are kept identical, except the number of
stories, and the homes are evaluated using differing rule sets. For the BA rule set the
energy savings increase if the number of stories is increased from 1-story to 2-story. For
all the other rule sets, the opposite occurs.
It is also important to point out that the 2-story, slab-on-grade home was used as the basis
for analysis. In other words, the 2-story, slab-on-grade Evaluated Home was iteratively
modified in each climate until their percentage savings with respect to the BA Reference
Home were as close as practical to 30%. Once this was accomplished, the exact same
envelope and equipment characteristics were incorporated into the 1-story and alternative
foundation home cases.
3.3.2
Foundation Type
Much like the number of stories, foundations are treated differently by the different rule
sets. Again, referring to Table 3.1, one can see that the distribution system efficiency in
the BA Reference Home is a function of foundation type. For single-story, slab-on-grade
construction, the Reference Home characteristics are the most lenient (i.e. they allow the
most room for improvement in the Actual Home). And for the basement home, the BA
Reference Home characteristics are the least stringent. In fact, they are perfect and allow
no room for improvement.
FSEC-CR-1650-06
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40
35%
35
30%
30
25%
25
20%
20
15%
15
10%
10
5%
5
0%
0
Chicago
1-Story
BA (Current)
Chicago
2-Story
Chicago
Crawl
HERS 2006
Source Energy Savings Over IECC (MBtu)
% Savings w.r.t. Specified Reference
Foundation Impacts: 30% BA Prototype Home
40%
Chicago
Basement
MBtu Save
Figure 3.9 Bar chart showing predicted energy savings for the 30% BA Prototype cases as a
function of the foundation type in Chicago.
Figure 3.9, above, illustrates the impact of foundation type, showing the predicted
percentage energy savings using both the current BA and the HERS 2006 rule sets. Also
shown by the magenta bar is the computed source energy savings in MBtu (106 Btu) as
compared with the IECC 2006 Reference Home. It is clear from this figure that the BA
rule set is treating foundations in exactly the opposite manner as the IECC and HERS
rule sets.
3.3.3
Fuel Type
Fuel type is treated in three different ways by the BA, the HERS and the IECC rule sets.
For the BA rule set, energy use and savings calculations are accomplished using source
energy use. For HERS, relative home energy ratings are calculated using the normalized
modified loads method, 6 and for the IECC, code compliance is determined using site
energy cost rather than either source or site energy use. However, for the purposes of this
analysis, all savings (percentage and MBtu) are calculated in accordance with the BA rule
set as source energy use savings.
6
Fairey, P., J. Tait, D. Goldstein, D. Tracey, M. Holtz, and R. Judkoff, "The HERS Rating Method and the
Derivation of the Normalized Modified Loads Method." Research Report No. FSEC-RR-54-00, Florida
Solar Energy Center, Cocoa, FL, October 11, 2000.
FSEC-CR-1650-06
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2
Energy Star 2006 BOP (Chicago: 2040 ft , 2-Story, Slab-on-Grade)
28
30%
27
25%
20%
26
15%
10%
25
5%
0%
Source Energy Savings Over IECC (MBtu)
% Savings w.r.t. Specified Reference
35%
24
Electric
BA (Current)
Gas
HERS 2006
MBtu Save
Figure 3.10 Bar chart showing differences between electricity and natural gas energy savings
predications for the 2006 ENERGY STAR home case in Chicago.
However, there are other differences in the treatment of fuel type among the different rule
sets. They can be generally illustrated using Figure 3.10, above. Using EPA’s
prescriptive standard for an ENERGY STAR home in Chicago, an all-electric heat pumpheated home and a natural gas furnace-heated home are evaluated. The natural gas home
also contains gas-fired hot water, stove and dryer systems. The envelope features of both
homes are identical. The results show that the all-electric ENERGY STAR home achieves
greater percentage savings using the BA rule set but the gas home achieves greater
savings using the HERS 2006 rule set. On the right-hand axis, the magenta bar shows the
source energy savings in MBtu for these homes as compared with the IECC Reference
Home energy use. These absolute energy savings also show that the gas home is saving
more total energy than the all-electric home with respect to 2006 code standards.
3.3.4
Internal Gains
Internal gains (iGains) make a significant difference in the heating and cooling energy
consumption of a home. The greater the internal gains the greater the cooling energy use
and the smaller the heating energy use. There are differences between the internal gains
assumptions in the BA rule set and the HERS and IECC rule sets. For the HERS and
IECC 2006 rule sets, internal gains are determined as a function of the conditioned floor
area (CFA) and the number of bedrooms (Nbr), as follows:
iGains = 17,900 + 23.8 * CFA + 4104 * Nbr
FSEC-CR-1650-06
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For the BA benchmark rule sets, internal gains are determined as a function of climate,
using climate multipliers for miscellaneous internal gains that vary from 0.77 to 1.11,
depending on climate. As a result, internal gains vary by climate for the BA rule set
while they are constant for the HERS and IECC rule sets.
2
BA 30% Prototype: 2-Story, 2040 ft , 3-Bedroom, Slab Homes
68
Sensible Internal Gains, Excepting Occupant Gains
Internal Gains (kBtu/day)
66
64
62
60
58
56
54
52
50
Miami
Zone 1
Houston
Zone 2
Charlotte
Zone 3
BA Internal Gains
St. Louis
Zone 4
Chicago
Zone 5
St. Paul
Zone 6
Duluth
Zone 7
Chicago
Gas
HERS Internal Gains
Figure 3.11 Bar chart showing internal gains (less occupant gains) for all electric homes in 7
climate zones and for gas home in Chicago (zone 5).
Figure 3.11 presents the total daily internal loads exclusive of occupant gains for the BA
rule set and the HERS rule set. While the HERS rule set is constant across climate zones,
the BA rule set varies from state to state. For Miami (and the remainder of Florida) the
BA climate multiplier for miscellaneous electric loads (MEL) is 0.94 and for Houston
(and the remainder of Texas), the multiplier is 1.11. For California, the multiplier is 0.77
and for New York it is 0.82. In the remaining states, the multiplier is 1.00.
The other item of interest shown in Figure 3.11 is the substantial increase in internal
gains for gas homes. Since sensible internal gains offset heating and increase cooling
energy uses, this difference results in the gas Evaluated Home being compared against a
different standard than the all-electric Evaluated Home. The result of this is to favor gas
homes in heating dominated climates but discourage them in cooling dominated climates.
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3.3.5
Energy Uses Other than Code Energy Uses
Codes have traditionally addressed only the energy uses associated with heating, cooling
and hot water. However, both the BA rule set and the HERS rule set include the lighting
and appliance energy uses in homes. For the purposes of this analysis, these “other”
energy uses, as defined by the BA rule set, have also been included in the IECC cases for
determining % savings so that the IECC rule set could be compared against the BA rule
set on a consistent basis. The exception to this is in the calculation of code e-Ratios,
where only heating, cooling and hot water are considered in accordance with the IECC
rule set.
For the HERS rule set, these “other” energy uses are also incorporated into the rule set,
however, they are slightly different that the “other” energy uses included in the BA rule
set. To be comprehensive, this report compares these “other” energy uses for the BA and
HERS Reference Homes for the 2-story, 2040 ft2, 3-bedroom, all-electric homes. Table
3.2 below presents the results of this comparison.
Table 3.2 Reference Home Lighting and Appliance Energy Uses for
All-electric Homes as Defined by the BA and HERS Rule Sets
"Other" Energy Uses
Hard wired lighting
Plug in lighting
Lighting subtotal
Refrigerator
Clothes washer
Clothes dryer
Dishwasher
Cooking
Other & plug
OA Ventilation
Total
BA
(kWh/yr)
1670
417
2087
669
105
835
206
604
3407
199
8111
HERS
(kWh/yr)
2086
774
891
145
447
3146
199
7688
Table 3.2 shows that, while there are sometimes significant differences in the individual
Reference Home energy uses between the two rule sets, there is a relatively small
difference (~5%) in the total lighting and appliance energy uses between the two rule
sets.
3.3.6
Home Size
To this point, results have been from only the medium sized home. However, the
analysis also considered home size. This home size analysis is accomplished using
slightly different homes than were used in the previous results. In order to keep
everything identical except the size of the homes, a set of 2-story “boxes” were created.
The box sizes were 20 ft x 30 ft, 30 ft x 40 ft and 40 ft by 45 ft. Each box had an 18%
window-to-floor area ratio with 40% of the windows facing east and west and 10% facing
north and south. Each box also contained identical envelope and equipment energy
FSEC-CR-1650-06
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efficiency features. These features were arrived at through a “calibration” of the 2,400
ft2 home to exactly meet the current BA 30% Prototype requirements.
Home Size Impacts: 2-story; All-Electric Homes; Miami, FL
Energy Savings (% of Specified Reference)
35%
32%
30%
30%
25%
25%
20%
16%
15%
14%
14%
11%
13%
10%
10%
5%
0%
3600 ft2
BA (Current)
2400 ft2
HERS 2006
1200 ft2
IECC 2006
Figure 3.12 Bar chart of percent energy savings as estimated by comparing the BA 30%
Prototype with the Reference Homes of the BA, HERS and IECC rule sets.
Figure 3.12 show the results of the home size analysis for homes located in Miami,
Florida. It is interesting to note that the BA results and the HERS and IECC results trend
in opposite directions. The BA rule set results in smaller savings predictions for smaller
homes and the HERS and IECC rule sets result in larger savings predictions for smaller
homes.
3.4
Higher Levels of Energy Efficiency (BA-50)
The BA 50% Prototype performance level was also examined in the study. Cooling
dominated, mixed and heating dominated climates were selected for this analysis. The
homes used were the 2-Story, 2040 ft2, slab-on-grade cases. They were modified to reach
the BA 50% Prototype performance level in each climate and the incremental revised
benchmark analysis discussed in Section 3.1 was performed for each case. The projected
savings for these homes were then compared across Reference homes.
FSEC-CR-1650-06
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2
BA 50% Prototype: 2-Story, 2040 ft , Slab Homes
% Savings w.r.t. Specified Reference
55%
50%
45%
40%
35%
30%
25%
20%
15%
10%
5%
0%
Miami
2-Story
BA (Current)
Charlotte
2-Story
HERS 2006
Duluth
2-Story
BA (Revised)
Figure 3.13 Bar chart of BA 50% Prototype homes showing cooling dominated, mixed and
heating dominated climate results. The Charlotte home required a 500 peak-watt PV system to
reach the 50% goal.
Figure 3.13 provides summary results from this analysis. In all cases the HERS and the
Revised BA rule sets showed less savings than the Current BA rule set. For Charlotte,
the HERS rule set shows projected savings very near the Current BA rule set, indicating
that the trends from the BA 30% Prototype analysis also pertain to the BA 50%
Prototype. Again, we see that a Revised BA rule set will result in the lowest projected
savings of the rule sets examined.
FSEC-CR-1650-06
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4
CONCLUSIONS
The conclusions that can be drawn from the analysis are closely related to the major rule
set differences presented in Section 2.2.2. These major rule set differences have been
examined on an individual basis by substituting each of the HERS Reference Home
characteristics, one-by-one, into the BA Reference Home and then evaluating the results
with respect to the BA 30% Prototype Homes used in this analysis (see also Table 3.1).
Figure 4.1 below presents results from the analysis, where the projected % savings using
each alternative Reference Home characteristic value is subtracted from the projected %
savings using the current BA Reference Home characteristic value (which is very near
30% for all cases).
2
Incremental BA Revisions: 2-Story, 2040ft , Slab Homes
4%
Change from BA % Savings
2%
0%
-2%
-4%
-6%
-8%
-10%
Miami
Zone 1
Ducts
Houston
Zone 2
Charlotte
Zone 3
tStat
St. Louis
Zone 4
Infil
Chicago
Zone 5
Windows
St. Paul
Zone 6
Duluth
Zone 7
Equip
Figure 4.1 Line graph of the change in projected savings for the BA 30% Prototype Home as
the characteristics of the BA Reference Home are revised, one-by-one, to correspond with the
HERS Reference Home values. A negative % savings value indicates that the revised value for
the BA Reference Home characteristic is more energy efficient than the current BA Reference
Home value used for the characteristic.
Figure 4.1 shows that differences in the Reference Home characteristics across BA and
HERS Reference Home rule sets are not necessarily consistent, either from characteristic
to characteristic or across climate zones. Some Reference Home characteristics provide
more change in southern climates and less in northern climates and some do the opposite.
One Reference Home characteristic, windows, actually changes in a way that causes the
mixed climate of Charlotte to stand out as very different from either cooling-dominated
or heating-dominated climates.
FSEC-CR-1650-06
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This study provides additional examples of differences among the standards that are
equally disparate. For example, Section 3.3 of the report highlights differences among
the standards for number of stories, foundation type, fuel type and home size that
illustrate that BA % savings can not be well correlated to the HERS Index, even within
the same climate.
A summary discussion of each of these major differences in Reference Home
characteristics follows:
•
Differences in the treatment of thermostat settings between the rule sets results in
the HERS rule set projecting savings that are about 2% less in the south to 1%
less in the north as compared with the BA rule set. These differences may at first
appears smaller than expected for a 2-3 oF thermostat revision, however, it is
important to again point out that identical thermostat schedules are used in both
the Reference and the Evaluated Homes, whether they are the current BA
thermostat settings or the revised thermostat settings from the HERS rules.
•
The line labeled ‘Ducts’ in Figure 4.1 shows the impacts of revising the BA
Reference Home distribution system efficiency. In southern climates, the revision
results in a less efficient Reference Home and in northern climates it results in a
more efficient Reference Home. However, these results apply only to the 2-story
slab-on-grade homes presented in Figure 4.1. In the BA rule set, distribution
system efficiency is heavily dependent on a number of parameters, including the
number of stories and the foundation type of the Actual Home and other home
and foundation types would achieve different results from those shown in
Figure 4.1.
The complexity of the differences between the rule sets makes it virtually
impossible to state with any certainty how results are impacted. In some cases,
projected savings are greater using the HERS rule set and in other cases projected
savings are greater. The data clearly show that it is much more difficult for BA
multi-story and basement homes to achieve large projected savings as compared
with single-story slab homes having the same building energy efficiency
attributes (see Figure 3.1).
•
The differences in Reference Home window treatment result in projected savings
that are not well correlated across climate types. For both cooling-dominated and
heating-dominated climates, the HERS and IECC Reference Home windows are
more energy efficient than the BA Reference Home windows. However, for
mixed climates like Charlotte, the BA Reference Home windows are more
efficient than the HERS and IECC Reference Home windows.
The differences are not as much related to window U-Factor as they are to
window solar heat gain coefficient (SHGC). For example, in Miami, the BA
Reference Home SHGC = 0.79, compared with a HERS Reference Home
window SHGC = 0.40. Heating dominated climates in zones 6, 7 and 8 (Chicago,
FSEC-CR-1650-06
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St. Paul and Duluth) are the opposite, with BA Reference Home window SHGC =
0.32 and HERS Reference Home window SHGC = 0.55. The result is that the
HERS Reference Home is more energy-efficient in both cooling-dominated and
heating-dominated climates. For Charlotte, the opposite is true and the BA
Reference Home windows are more energy efficient than the HERS and IECC
Reference Home windows.
•
Equipment standard differences among rule sets appear reasonably well behaved.
There are greater differences in cooling dominated climates compared with
heating dominated climates because the increase in Reference Home equipment
efficiency is greater for cooling systems than for heating systems. In fact, for gasfired furnaces, there is no difference in Reference Home heating efficiencies
between the various rule sets.
•
The treatment of mechanical ventilation and infiltration is different in both
Reference and Evaluated Home rule sets. The BA rule set adds the full
ventilation air flow to a fairly high infiltration air exchange rate, while the HERS
and IECC rule sets for Reference Homes do not. When the Actual Home is
mechanically vented, the HERS and IECC Reference Home rule sets add
additional fan energy to their Reference Homes but they do not add additional
mechanical ventilation air flow because the Reference Home natural infiltration
rates are assumed to be sufficient. The fan energy is added so that mechanical
ventilation is not penalized in the Evaluated Home, which has the same type of
mechanical ventilation as the Actual Home. As illustrated by Figure 4.1, the BA
rule set provides substantially more benefit to home tightening and unbalanced
mechanical ventilation in heating-dominated climates.
The overall conclusion from the analysis is that, due to the profound differences between
rule sets, it is not possible to define a consistent correlation between the BA % savings
value and the HERS or IECC figures of merit (the HERS Index or the Code e-Ratio).
The changes in projected savings are so significant and their magnitudes so dependent on
such a large number of interacting home features (e.g. foundation type, number of stories,
home size, fuel type, etc.) that it is not possible to translate any given BA % savings
value into a HERS Index and vise versa.
FSEC-CR-1650-06
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5
RECOMMENDATIONS
It is difficult to make recommendations based on this analysis. There can be pros and
cons for any given rule set used to project energy savings. For example, the BA rule set
was originally developed to measure progress toward a set of U.S. DOE energy savings
milestones called Joules. The intent was to have a consistent standard of performance
tied to mid 1990’s era home standards. However, in the mid 1990’s there were no
definitive code standards for windows that are analogous to those that became effective
in 1998. In addition, there were no standards or rule sets in the mid 1990’s for the
evaluation of distribution system efficiency, mechanical ventilation or lighting and
appliances in homes.
Since the original objective of this study – to establish a correlation between the BA %
savings value and the HERS Index value – could not be accomplished, there appear to be
three potential options for moving forward. While options may not be considered
recommendations in the conventional sense of the term, they, along with their advantages
and disadvantages, are presented below:
1. Maintain the current BA rule set. This option allows BA program milestones to
continue to be measured from a constant reference point. While this reference
point can not be directly correlated to current codes or to HERS, it does allow
program goals to remain consistent with past objectives. However, this advantage
also works as a disadvantage. Potential builder partners can not be told with
certainty how much better than code there homes will be. Thus, they are left in a
bit of a quandary as to how they can advertise these homes in a way that is simply
explained to their potential customers.
Another disadvantage of proceeding with this option is that the current BA rule
set appears to significantly advantage certain climates and significantly
disadvantage others, at least with respect to current national model building codes
and standards. For example, the BA 30% Prototype home in Charlotte, NC
qualifies for the EPAct 2005 federal tax credit. At the same time, the BA 30%
Prototype home in Duluth, MN, is only 8% more efficient than the IECC 2006 for
that climate.
2. Revise the BA rule set. While revising the BA rule set may bring it more in line
with alternative, more current rule sets, the analysis presented here did not show
that this would result in complete correlation between revised BA % savings
values and the HERS Index (or Code e-Ratio). The revised BA rule set examined
here consistently resulted in lower % savings values than the HERS rule set (see
Figure 3.3). Thus, adopting the revised BA rule set will cause BA program goals
to appear significantly more difficult than code-based programs. While this may
be true because code-based programs do not include lighting and appliance
energy use while BA programs do, it will make achieving the BA 30% savings
goal extremely difficult for BA builder partners, especially in heating dominated
FSEC-CR-1650-06
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climates. Note that the current BA 30% Prototype would only achieve 8%
savings under a revised BA rule set in Duluth (Figure 3.3).
3. Migrate to the HERS Index. A large disadvantage of migrating to the HERS
Index is that it would change the basis of BA program savings goals and
milestones. Of course, the previous option, revising the BA rule set, would do the
same. There are, however, some advantages of this option. The HERS Index is
widely used as a performance metric. It is used as the basis for the ENERGY STAR
new homes program and other emerging national programs like USGBC’s pilot
LEED-H program. The HERS rule set also forms the basis for the EPAct 2005
federal tax credit for highly efficient new homes. A significant advantage of the
HERS rule set is that it is a consensus-based national standard.
As a metric, the HERS Index includes all of the energy uses of a home. This is
one of the basic tenets of the BA program – that whole home energy use is the
comparison basis of the program. While changing the BA program standard to
the IECC rule set would violate this tenet, changing to the HERS rule set standard
would not. The HERS rule set also specifies a methodology to “score” the use of
on-site energy production, whether by solar, wind or other “free” fuel resources
or by highly efficient on-site conventional fuel technologies like micro-turbines
and small combined heat and power plants.
A disadvantage of the HERS Index is that the “scoring method” used by the rule
set does not use energy use as its metric. The metric used by the HERS rule set is
called the normalized modified loads method. 7 It was derived as a compromise
consensus method of avoiding the fight between site energy use and source
energy use. It can be shown to reasonably reflect energy cost in a market where
the ratio between site costs for electricity and natural gas are near the ratio of
3 to 1.
Finally, one advantage of using the HERS Index is that it can be explained fairly
simply – the “American Standard New Home” has an index of 100 and a home
that uses no purchased energy has an index of 0. In other words, zero is zero and
anything greater than 100 probably doesn’t meet current minimum energy
standards.
7
Fairey, P., J. Tait, D. Goldstein, D. Tracey, M. Holtz, and R. Judkoff, "The HERS Rating Method and the
Derivation of the Normalized Modified Loads Method." Research Report No. FSEC-RR-54-00, Florida
Solar Energy Center, Cocoa, FL, October 11, 2000.
FSEC-CR-1650-06
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6
REFERENCES
EPA, Energy Star Qualified Homes: National Builder Option Package, U.S.
Environmental Protection Agency, Washington, DC, July 1, 2006. Online at
http://www.energystar.gov/ia/partners/bldrs_lenders_raters/downloads/NatBOPTRK_060206.pdf
Fairey, P., J. Tait, D. Goldstein, D. Tracey, M. Holtz, and R. Judkoff, "The HERS Rating
Method and the Derivation of the Normalized Modified Loads Method."
Research Report No. FSEC-RR-54-00, Florida Solar Energy Center, Cocoa, FL,
October 11, 2000. Online at http://www.fsec.ucf.edu/bldg/pubs/hers_meth/index.htm
NREL, Building America Research Benchmark Definition, National Renewable Energy
Laboratory, Golden, CO, December 29, 2004. Online at
http://www.eere.energy.gov/buildings/building_america/pa_resources.html
NREL, Building America Analysis Spreadsheet, National Renewable Energy Laboratory,
Golden, CO, May 6, 2006. Online at
http://www.eere.energy.gov/buildings/building_america/pa_resources.html
RESNET, 2006 Mortgage Industry Notional Home Energy Rating Systems Standards,
Residential Energy Services Network, Oceanside, CA, August 21, 2006. Online
at http://www.resnet.us/standards/RESNET_Standards-2006.pdf
FSEC-CR-1650-06
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Appendix A
Selected House Plans and Elevations
Figure A-1. First (on left) and second (on right) floor plan for 2040 ft2 home used as the medium-sized model for the majority of
the cases in the analysis.
FSEC-CR-1650-06
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Figure A-2 Front elevation for two-story 2040 ft2 model home.
Figure A-3 Three-dimensional rendering of two story 2040 ft2 model home.
FSEC-CR-1650-06
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Figure A-4 Floor plan for single-story 2040 ft2 home.
FSEC-CR-1650-06
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Figure A-5 Front elevation of single-story 2040 ft2 model home
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Appendix B
Housing Characteristics
The following building construction data and statistics for finished single-family homes
were extracted from the U.S. Census Bureau site (http://www.census.gov/). The data was
used to generate the following charts for the one-year period ending in June 2005.
Climate Region Construction Activity
Top 50 Permit Areas
Breakdown by Climate Zone
Mixed-Dry
Marine
0%
6%
MixedCold
Humid
Mixed-Humid
18%
32%
Hot Dry
Hot -humid
Cold
Marine
Mixed-Dry
Hot -humid
Hot Dry
30%
14%
For each of the top 50 metropolitan singlefamily home construction areas, a climate
region was designated based on the county
listed under the Building America climate
region listing (version 2, Nov. 6, 2003). The
resulting percentage breakdown can be
viewed in the chart shown at right. Mixed
(32%) and Hot-Humid (30%) areas represent
the larger regions of construction activity for
single-family homes built during 2004-2005
Single-family Home Sizes
The chart to the right displays a
breakdown as percentage of
home sizes built during 2004-05.
Seventy-eight percent of the
homes were of at least 1600 ft2
or larger. Smaller homes
including those less than 1200 ft2
account for 22% of the total
built.
FSEC-CR-1650-06
2004, 2000 & 1990 Single-Family Homes
350
300
Completed Homes (000s)
The bar chart at right displays
the number of completed
homes by size with the rightmost range illustrating the
amount of homes with
conditioned living area larger
than 3000 ft2. The sampled
statistics show the difference in
the amount of homes built for
the respective years, but most
notably the increased change of
number of homes with square
footage larger than 3000 ft2
when compared to 1990.
250
2004
200
1990
150
2000
100
50
0
<1200
1200-1599 1600-1999 2000-2399 2400-2999
>3000
Square Feet of Floor Area (Sq. ft.)
2004 Single-Family Homes
Percentange of Total Completed by Size (Sq. ft.)
5%
20%
17%
19%
21%
<1200
1200-1599
1600-1999
2000-2399
2400-2999
>3000
18%
44
Square Feet of Floor Area by
Region
2004 Single-Family Homes
Square Feet of Floor Area by Region
160
140
Completed Homes (000s)
The number of completed homes (by
size) continues to be dominant in the
South region as shown in the bar-chart
figure at right. The amount of
completed homes built in the NorthEast region show the least amount of
building activity.
120
<1200
100
1200-1599
1600-1999
80
2000-2399
2400-2999
60
>3000
40
20
0
North East
Midwest
South
West
Number of Stories
The number of stories for those singlefamily homes built during 2004-05
appear to be about equal for all regions
except for the Northeast region, where
the 2-story is the most dominant.
2004 Homes Completed - Number of Stories
100%
90%
Percentage of Homes
80%
70%
60%
1 Story
50%
2>Story
Spilt Level
40%
Furthermore, the south region is the
only region that shows a slight
percentage increase on one-story
homes (about 3%) over two-story
homes.
30%
20%
10%
0%
North East
Midw est
South
West
Foundation Types
FSEC-CR-1650-06
2004 Homes Completed - Foundation Type
100%
90%
80%
Percentage of Homes
The type of foundation construction
for single-family buildings on the four
regions of the country can be
examined in the side chart. Basement
type homes continue to dominate in
the Northeast (83%) and Mid-West
(76%) regions. Slab foundations are
the dominant construction method in
the South (70%) and West (65%)
regions of the country. Crawl
foundation types in the South and the
West regions represent 17% and 20%
respectively.
70%
60%
Basement
50%
Slab
40%
Crawl
30%
20%
10%
0%
North East
Midwest
South
West
45
Building Wall Envelope Material
Vinyl siding (38%) appears to be the
dominant exterior wall material used
in today's construction of single family homes followed by stucco
(22%). Brick (19%) follow as the
third material utilized in wall
construction as can observed in the
South region category on the next
plot shown below.
2004 Single -Family Home s Wall Type s
40%
Percentage of Exterior Wall Type
35%
30%
25%
Series1
20%
15%
10%
5%
0%
Brick
Wood
Stucco
V ynil Siding
A luminum
siding
Other
90%
80%
Percentage of Wall type (%)
70%
60%
Brick
Wood
50%
Stucco
Vynil Siding
40%
Aluminum Siding
Other
30%
20%
Vinyl siding also dominates as
the preferred exterior wall
material used in the Northeast
and Midwest. However, stucco
is clearly the dominant exterior
wall material utilized in the
West.
10%
0%
North East
Midwest
South
West
Heating Fuel
2004 New Single-Family Heating Fuel by Region
400
350
Number of houses completed (000s)
The type of fuel utilized to heat
single-family homes constructed
during the 2004-05 period can be
examined in the chart below.
Electric heating (54.3%)
dominates in the South region
and natural gas represents the
majority throughout the rest of
the country.
300
250
Gas
Electric
200
Oil
Other/None
150
100
50
0
North East
FSEC-CR-1650-06
Midwest
South
W est
46